Glycosaminoglycans are high molecular weight, linear, polysaccharides which are major constituents of extracellular matrix. In addition, glycosaminoglycans are found in association with the surface of cells. In some cases this association is quite loose and the material can be washed off; in other cases, however, the association is very firm and these glycosaminoglycans are presumed to represent true integral membrane components. Human fibroblasts in culture undergo a period of rapid proliferation which is followed by a decline in the rate of proliferation and the eventual demise of the culture. It has been suggested that this phenomenon may represent aging at the cellular level. It is the overall objective of this project to determine the composition and structural characteristics of glycosaminoglycans produced by cultured fibroblasts of different proliferative potentials (in vitro age) and from donors of differing chronological age, in order to understand the source of those changes in connective tissue with age which can affect the function of tissues.